On Sun, 28 Nov 2004 21:25:24 -0500, Jack Tanner <[EMAIL PROTECTED]>
wrote:
>This is a best practices / style question.
>
>The way I use RODBC is I something like this:
>
> > foo <- sqlQuery(db, "select * from foo")
> > apply(foo, 1, function{...})
>
>That is, I use apply to iterate over each result -- row -- in the
>RODBC-produced dataframe. Is this how one generally wants to do this?
>
>My concern is that when apply iterates over the rows, it uses
>as.matrix() to convert the dataframe to a character representation of
>itself. Thus my database's carefully planned data types (that RODBC
>carefully preserved when returning query results) get completely lost as
>I process the data. I've taken to judiciously sprinkling as.numeric()
>and friends here and there, but this is just begging for bugs.
>
>In other words, what is the smart way to process a dataframe by rows? Or
>is there, by chance, a specific technique or practice that is available
>for RODBC results but not for dataframes in general?
I would just use a for() loop if I didn't care about the speed too
much. If I did, I'd avoid dealing with rows of dataframes: access
using dataframe indexing is slow. Depending what your function is,
you're probably better off extracting the columns of the dataframe as
vectors, and working with those.
Duncan Murdoch
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